The current literature contains a wealth of information directed to polypeptide purification methodologies, which primarily involve chromatographic approaches as well as membrane filtration techniques. However, effective methods for the purification of modified polypeptides (e.g., PEGylated polypeptides) are not well known. The modification of polypeptides with polymeric moieties causes a significant shift in the chemical and physical properties of those polypeptides. Methods, which are useful for the purification of non-modified polypeptides are not necessarily effective in capturing their modified versions.
When a glycosylated or non-glycosylated polypeptide is subjected to a chemical modification reaction, side-products may be formed in addition to the desired modified polypeptide. In order to isolate a desired product from a reaction mixture, the process must not only be suitable to remove chemical reagents, but must also be capable of removing unwanted side-products. This is especially important when the polypeptide is to be used as a therapeutic agent. Polypeptide modification technologies, which rely on the specificity of enzymes, may result in a reaction product that is characterized by improved homogeneity when compared to other chemical methods. However, expression of a recombinant polypeptide in a cell (e.g., bacterial, insect, yeast or mammalian cell) typically results in a polypeptide population that, at leas to some extend, is characterized by a variety of glycan structures. Subsequent modification of the polypeptide, e.g., via those glycans, results in a heterogenous product. Although remodeling glycan structures prior to chemical or enzymatic modification of the polypeptide can significantly improve the quality of the product, a certain degree of heterogeneity remains. Hence, a need exists for production processes designed to isolate a desired polypeptide conjugate from a reaction mixture that may not only contain chemical reagents (e.g., those derived from unreacted modifying groups) and/or catalytic enzymes, but may also include polypeptide conjugate by-products. The present invention addresses these and other needs.